Dust from green wood can be just as explosive as sawdust from beetle kill timber, says WorkSafeBC.

WorksSafeBC is still investigating the cause of explosions and fires at two B.C. sawmills earlier this year that killed three people.

On January 20, an explosion and fire at Babine Forest ProductsLtd. in Burns Lake levelled the mill, killing two local residents and injuring 19 others.

And in April the Lakeland Mills in Prince George also went up in flames after an explosion, killing one employee and hospitalized 24 workers.

Both mills had been milling pine harvested from areas where trees have been killed by the mountain pine beetle. Because the trees are dead when harvested, they are drier than lives trees, which drove speculation that the mill explosions were caused by the excessive dryness of sawdust from pine beetle wood.

That may still prove to be the case when the investigation concludes, which is expected to be sometime in the fall.

In the meantime, however, WorkSafeBC underscored the need for all sawmills in B.C. to take dust control seriously, no matter what kind of fibre supply they are using.

WorkSafeBC conducted a lab test on sawdust from green wood and found that it is as combustible as pine beetle kill when the moisture content of the dust is below 5% and the particle size is less than 75 micrometres.

The implications of those findings is that mills that are not processing pine beetle kill must not be complacent about addressing dust issues in their mills.

"The evidence we're receiving as the investigation proceeds is that all dust under certain circumstances can have that volatility," said Jeff Dolan, WorkSafeBC's director of investigations.

"Those mills that are still in operation can't consider themselves to be excluded because they're not milling beetle kill wood.

"If there is one mill operating out there that feels they are exempt because they're not milling beetle kill wood, that's who we want to be communicating with today."

Following the explosions, WorkSafeBC issued directions to the lumber industry to implement dust management programs, if they weren't already, and began inspecting lumber mills.

The inspection program was expanded in July to include other wood processors other than lumber mills – such as pellet and planer mills. A third phase will expand the inspections to other industries that generate dust from wood and other sources.